diff --git a/backend/app/alembic/versions/66abc97f3782_user_id_from_uuid_to_int.py b/backend/app/alembic/versions/66abc97f3782_user_id_from_uuid_to_int.py
new file mode 100644
index 000000000..0035b705b
--- /dev/null
+++ b/backend/app/alembic/versions/66abc97f3782_user_id_from_uuid_to_int.py
@@ -0,0 +1,156 @@
+"""user_id from uuid to int
+
+Revision ID: 66abc97f3782
+Revises: 60b6c511a485
+Create Date: 2025-06-16 11:05:36.196795
+
+"""
+from alembic import op
+import sqlalchemy as sa
+import sqlmodel.sql.sqltypes
+
+
+# revision identifiers, used by Alembic.
+revision = "66abc97f3782"
+down_revision = "60b6c511a485"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    conn = op.get_bind()
+
+    # Drop foreign key constraints
+    conn.execute(
+        sa.text("ALTER TABLE document DROP CONSTRAINT document_owner_id_fkey;")
+    )
+    conn.execute(
+        sa.text("ALTER TABLE collection DROP CONSTRAINT collection_owner_id_fkey;")
+    )
+    conn.execute(
+        sa.text("ALTER TABLE projectuser DROP CONSTRAINT projectuser_user_id_fkey;")
+    )
+    conn.execute(sa.text("ALTER TABLE apikey DROP CONSTRAINT apikey_user_id_fkey;"))
+
+    # Drop primary key constraint on "user" table
+    conn.execute(sa.text('ALTER TABLE "user" DROP CONSTRAINT user_pkey;'))
+
+    # Create mapping table from UUID to INT
+    conn.execute(
+        sa.text(
+            """
+        CREATE TABLE uuid_to_int_map (
+            user_id_uuid UUID PRIMARY KEY,
+            user_id_int INT GENERATED ALWAYS AS IDENTITY
+        );
+    """
+        )
+    )
+
+    # Populate mapping table
+    conn.execute(
+        sa.text('INSERT INTO uuid_to_int_map (user_id_uuid) SELECT id FROM "user";')
+    )
+
+    # Add new_id to user table and populate it
+    conn.execute(sa.text('ALTER TABLE "user" ADD COLUMN new_id INT;'))
+    conn.execute(
+        sa.text(
+            """
+        UPDATE "user" SET new_id = uuid_map.user_id_int
+        FROM uuid_to_int_map uuid_map
+        WHERE "user".id = uuid_map.user_id_uuid;
+    """
+        )
+    )
+
+    # document
+    conn.execute(sa.text("ALTER TABLE document ADD COLUMN new_owner_id INT;"))
+    conn.execute(
+        sa.text(
+            """
+        UPDATE document SET new_owner_id = uuid_map.user_id_int
+        FROM uuid_to_int_map uuid_map
+        WHERE document.owner_id = uuid_map.user_id_uuid;
+    """
+        )
+    )
+
+    # collection
+    conn.execute(sa.text("ALTER TABLE collection ADD COLUMN new_owner_id INT;"))
+    conn.execute(
+        sa.text(
+            """
+        UPDATE collection SET new_owner_id = uuid_map.user_id_int
+        FROM uuid_to_int_map uuid_map
+        WHERE collection.owner_id = uuid_map.user_id_uuid;
+    """
+        )
+    )
+
+    # projectuser
+    conn.execute(sa.text("ALTER TABLE projectuser ADD COLUMN new_user_id INT;"))
+    conn.execute(
+        sa.text(
+            """
+        UPDATE projectuser SET new_user_id = uuid_map.user_id_int
+        FROM uuid_to_int_map uuid_map
+        WHERE projectuser.user_id = uuid_map.user_id_uuid;
+    """
+        )
+    )
+
+    # apikey
+    conn.execute(sa.text("ALTER TABLE apikey ADD COLUMN new_user_id INT;"))
+    conn.execute(
+        sa.text(
+            """
+        UPDATE apikey SET new_user_id = uuid_map.user_id_int
+        FROM uuid_to_int_map uuid_map
+        WHERE apikey.user_id = uuid_map.user_id_uuid;
+    """
+        )
+    )
+
+    # Drop old columns and rename new ones
+    conn.execute(sa.text("ALTER TABLE document DROP COLUMN owner_id;"))
+    conn.execute(
+        sa.text("ALTER TABLE document RENAME COLUMN new_owner_id TO owner_id;")
+    )
+
+    conn.execute(sa.text("ALTER TABLE collection DROP COLUMN owner_id;"))
+    conn.execute(
+        sa.text("ALTER TABLE collection RENAME COLUMN new_owner_id TO owner_id;")
+    )
+
+    conn.execute(sa.text("ALTER TABLE projectuser DROP COLUMN user_id;"))
+    conn.execute(
+        sa.text("ALTER TABLE projectuser RENAME COLUMN new_user_id TO user_id;")
+    )
+
+    conn.execute(sa.text("ALTER TABLE apikey DROP COLUMN user_id;"))
+    conn.execute(sa.text("ALTER TABLE apikey RENAME COLUMN new_user_id TO user_id;"))
+
+    conn.execute(sa.text('ALTER TABLE "user" DROP COLUMN id;'))
+    conn.execute(sa.text('ALTER TABLE "user" RENAME COLUMN new_id TO id;'))
+
+    # Re-add primary key
+    conn.execute(sa.text('ALTER TABLE "user" ADD PRIMARY KEY (id);'))
+
+    # Create sequence for new integer IDs
+    conn.execute(sa.text('CREATE SEQUENCE user_id_seq START 1 OWNED BY "user".id;'))
+    conn.execute(
+        sa.text(
+            "ALTER TABLE \"user\" ALTER COLUMN id SET DEFAULT nextval('user_id_seq');"
+        )
+    )
+    conn.execute(
+        sa.text("SELECT setval('user_id_seq', (SELECT MAX(id) FROM \"user\"));")
+    )
+
+    # Drop mapping table
+    conn.execute(sa.text("DROP TABLE uuid_to_int_map;"))
+
+
+def downgrade():
+    pass
diff --git a/backend/app/alembic/versions/8e7dc5eab0b0_add_fk_constraint_to_user_id_columns.py b/backend/app/alembic/versions/8e7dc5eab0b0_add_fk_constraint_to_user_id_columns.py
new file mode 100644
index 000000000..09fe3ef99
--- /dev/null
+++ b/backend/app/alembic/versions/8e7dc5eab0b0_add_fk_constraint_to_user_id_columns.py
@@ -0,0 +1,55 @@
+"""add fk constraint to user id columns
+
+Revision ID: 8e7dc5eab0b0
+Revises: 66abc97f3782
+Create Date: 2025-06-16 11:08:46.893642
+
+"""
+from alembic import op
+import sqlalchemy as sa
+import sqlmodel.sql.sqltypes
+
+
+# revision identifiers, used by Alembic.
+revision = "8e7dc5eab0b0"
+down_revision = "66abc97f3782"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.alter_column("apikey", "user_id", existing_type=sa.INTEGER(), nullable=False)
+    op.create_foreign_key(
+        None, "apikey", "user", ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column(
+        "collection", "owner_id", existing_type=sa.INTEGER(), nullable=False
+    )
+    op.create_foreign_key(
+        None, "collection", "user", ["owner_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("document", "owner_id", existing_type=sa.INTEGER(), nullable=False)
+    op.create_foreign_key(
+        None, "document", "user", ["owner_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column(
+        "projectuser", "user_id", existing_type=sa.INTEGER(), nullable=False
+    )
+    op.create_foreign_key(
+        None, "projectuser", "user", ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_constraint(None, "projectuser", type_="foreignkey")
+    op.alter_column("projectuser", "user_id", existing_type=sa.INTEGER(), nullable=True)
+    op.drop_constraint(None, "document", type_="foreignkey")
+    op.alter_column("document", "owner_id", existing_type=sa.INTEGER(), nullable=True)
+    op.drop_constraint(None, "collection", type_="foreignkey")
+    op.alter_column("collection", "owner_id", existing_type=sa.INTEGER(), nullable=True)
+    op.drop_constraint(None, "apikey", type_="foreignkey")
+    op.alter_column("apikey", "user_id", existing_type=sa.INTEGER(), nullable=True)
+    # ### end Alembic commands ###
diff --git a/backend/app/api/routes/api_keys.py b/backend/app/api/routes/api_keys.py
index 8d6905908..977dd02a5 100644
--- a/backend/app/api/routes/api_keys.py
+++ b/backend/app/api/routes/api_keys.py
@@ -20,7 +20,7 @@
 @router.post("/", response_model=APIResponse[APIKeyPublic])
 def create_key(
     project_id: int,
-    user_id: uuid.UUID,
+    user_id: int,
     session: Session = Depends(get_db),
     current_user: User = Depends(get_current_active_superuser),
 ):
diff --git a/backend/app/api/routes/onboarding.py b/backend/app/api/routes/onboarding.py
index fa8559d55..f267e37f6 100644
--- a/backend/app/api/routes/onboarding.py
+++ b/backend/app/api/routes/onboarding.py
@@ -40,7 +40,7 @@ class OnboardingRequest(BaseModel):
 class OnboardingResponse(BaseModel):
     organization_id: int
     project_id: int
-    user_id: uuid.UUID
+    user_id: int
     api_key: str
 
 
diff --git a/backend/app/api/routes/project_user.py b/backend/app/api/routes/project_user.py
index e5723891a..17bd5b8aa 100644
--- a/backend/app/api/routes/project_user.py
+++ b/backend/app/api/routes/project_user.py
@@ -22,7 +22,7 @@
 )
 def add_user(
     request: Request,
-    user_id: uuid.UUID,
+    user_id: int,
     is_admin: bool = False,
     session: Session = Depends(get_db),
     current_user: UserProjectOrg = Depends(verify_user_project_organization),
@@ -81,7 +81,7 @@ def list_project_users(
 )
 def remove_user(
     request: Request,
-    user_id: uuid.UUID,
+    user_id: int,
     session: Session = Depends(get_db),
     current_user: UserProjectOrg = Depends(verify_user_project_organization),
 ):
diff --git a/backend/app/api/routes/users.py b/backend/app/api/routes/users.py
index 60a043bc6..956461010 100644
--- a/backend/app/api/routes/users.py
+++ b/backend/app/api/routes/users.py
@@ -160,7 +160,7 @@ def register_user(session: SessionDep, user_in: UserRegister) -> Any:
 
 @router.get("/{user_id}", response_model=UserPublic, include_in_schema=False)
 def read_user_by_id(
-    user_id: uuid.UUID, session: SessionDep, current_user: CurrentUser
+    user_id: int, session: SessionDep, current_user: CurrentUser
 ) -> Any:
     """
     Get a specific user by id.
@@ -185,7 +185,7 @@ def read_user_by_id(
 def update_user_endpoint(
     *,
     session: SessionDep,
-    user_id: uuid.UUID,
+    user_id: int,
     user_in: UserUpdate,
 ) -> Any:
     """
@@ -215,7 +215,7 @@ def update_user_endpoint(
     include_in_schema=False,
 )
 def delete_user(
-    session: SessionDep, current_user: CurrentUser, user_id: uuid.UUID
+    session: SessionDep, current_user: CurrentUser, user_id: int
 ) -> Message:
     """
     Delete a user.
diff --git a/backend/app/crud/api_key.py b/backend/app/crud/api_key.py
index 5a4f3a047..905d0a1b1 100644
--- a/backend/app/crud/api_key.py
+++ b/backend/app/crud/api_key.py
@@ -19,7 +19,7 @@ def generate_api_key() -> tuple[str, str]:
 
 
 def create_api_key(
-    session: Session, organization_id: int, user_id: uuid.UUID, project_id: int
+    session: Session, organization_id: int, user_id: int, project_id: int
 ) -> APIKeyPublic:
     """
     Generates a new API key for an organization and associates it with a user.
diff --git a/backend/app/crud/collection.py b/backend/app/crud/collection.py
index 830466833..7b91f4fbd 100644
--- a/backend/app/crud/collection.py
+++ b/backend/app/crud/collection.py
@@ -11,7 +11,7 @@
 
 
 class CollectionCrud:
-    def __init__(self, session: Session, owner_id: UUID):
+    def __init__(self, session: Session, owner_id: int):
         self.session = session
         self.owner_id = owner_id
 
diff --git a/backend/app/crud/document.py b/backend/app/crud/document.py
index db1dce4d0..32b59f484 100644
--- a/backend/app/crud/document.py
+++ b/backend/app/crud/document.py
@@ -8,7 +8,7 @@
 
 
 class DocumentCrud:
-    def __init__(self, session: Session, owner_id: UUID):
+    def __init__(self, session: Session, owner_id: int):
         self.session = session
         self.owner_id = owner_id
 
diff --git a/backend/app/crud/project_user.py b/backend/app/crud/project_user.py
index 8a3d88350..3b5dedd1d 100644
--- a/backend/app/crud/project_user.py
+++ b/backend/app/crud/project_user.py
@@ -6,7 +6,7 @@
 from app.core.util import now
 
 
-def is_project_admin(session: Session, user_id: str, project_id: int) -> bool:
+def is_project_admin(session: Session, user_id: int, project_id: int) -> bool:
     """
     Checks if a user is an admin of the given project.
     """
@@ -23,7 +23,7 @@ def is_project_admin(session: Session, user_id: str, project_id: int) -> bool:
 
 # Add a user to a project
 def add_user_to_project(
-    session: Session, project_id: uuid.UUID, user_id: uuid.UUID, is_admin: bool = False
+    session: Session, project_id: int, user_id: int, is_admin: bool = False
 ) -> ProjectUserPublic:
     """
     Adds a user to a project.
@@ -47,9 +47,7 @@ def add_user_to_project(
     return ProjectUserPublic.model_validate(project_user)
 
 
-def remove_user_from_project(
-    session: Session, project_id: uuid.UUID, user_id: uuid.UUID
-) -> None:
+def remove_user_from_project(session: Session, project_id: int, user_id: int) -> None:
     """
     Removes a user from a project.
     """
@@ -70,7 +68,7 @@ def remove_user_from_project(
 
 
 def get_users_by_project(
-    session: Session, project_id: uuid.UUID, skip: int = 0, limit: int = 100
+    session: Session, project_id: int, skip: int = 0, limit: int = 100
 ) -> tuple[list[ProjectUserPublic], int]:
     """
     Returns paginated users in a given project along with the total count.
@@ -94,9 +92,7 @@ def get_users_by_project(
 
 
 # Check if a user belongs to an at least one project in organization
-def is_user_part_of_organization(
-    session: Session, user_id: uuid.UUID, org_id: int
-) -> bool:
+def is_user_part_of_organization(session: Session, user_id: int, org_id: int) -> bool:
     """
     Checks if a user is part of at least one project within the organization.
     """
diff --git a/backend/app/models/api_key.py b/backend/app/models/api_key.py
index 188f529b3..22387e1bf 100644
--- a/backend/app/models/api_key.py
+++ b/backend/app/models/api_key.py
@@ -14,9 +14,7 @@ class APIKeyBase(SQLModel):
     project_id: int = Field(
         foreign_key="project.id", nullable=False, ondelete="CASCADE"
     )
-    user_id: uuid.UUID = Field(
-        foreign_key="user.id", nullable=False, ondelete="CASCADE"
-    )
+    user_id: int = Field(foreign_key="user.id", nullable=False, ondelete="CASCADE")
     key: str = Field(
         default_factory=lambda: secrets.token_urlsafe(32), unique=True, index=True
     )
diff --git a/backend/app/models/collection.py b/backend/app/models/collection.py
index 1e74d29c7..2d7ea2a5e 100644
--- a/backend/app/models/collection.py
+++ b/backend/app/models/collection.py
@@ -12,7 +12,7 @@ class Collection(SQLModel, table=True):
         default_factory=uuid4,
         primary_key=True,
     )
-    owner_id: UUID = Field(
+    owner_id: int = Field(
         foreign_key="user.id",
         nullable=False,
         ondelete="CASCADE",
diff --git a/backend/app/models/document.py b/backend/app/models/document.py
index c0c02ee75..71da74c1b 100644
--- a/backend/app/models/document.py
+++ b/backend/app/models/document.py
@@ -12,7 +12,7 @@ class Document(SQLModel, table=True):
         default_factory=uuid4,
         primary_key=True,
     )
-    owner_id: UUID = Field(
+    owner_id: int = Field(
         foreign_key="user.id",
         nullable=False,
         ondelete="CASCADE",
diff --git a/backend/app/models/project_user.py b/backend/app/models/project_user.py
index cbc18efd5..57028436f 100644
--- a/backend/app/models/project_user.py
+++ b/backend/app/models/project_user.py
@@ -11,9 +11,7 @@ class ProjectUserBase(SQLModel):
     project_id: int = Field(
         foreign_key="project.id", nullable=False, ondelete="CASCADE"
     )
-    user_id: uuid.UUID = Field(
-        foreign_key="user.id", nullable=False, ondelete="CASCADE"
-    )
+    user_id: int = Field(foreign_key="user.id", nullable=False, ondelete="CASCADE")
     is_admin: bool = Field(
         default=False, nullable=False
     )  # Determines if user is an admin of the project
diff --git a/backend/app/models/user.py b/backend/app/models/user.py
index f39c6161c..66a7e932c 100644
--- a/backend/app/models/user.py
+++ b/backend/app/models/user.py
@@ -46,7 +46,7 @@ class UpdatePassword(SQLModel):
 
 # Database model, database table inferred from class name
 class User(UserBase, table=True):
-    id: uuid.UUID = Field(default_factory=uuid.uuid4, primary_key=True)
+    id: int = Field(default=None, primary_key=True)
     hashed_password: str
     documents: list["Document"] = Relationship(
         back_populates="owner", cascade_delete=True
@@ -61,7 +61,7 @@ class User(UserBase, table=True):
 
 
 class UserOrganization(UserBase):
-    id: uuid.UUID
+    id: int
     organization_id: int | None
 
 
@@ -71,7 +71,7 @@ class UserProjectOrg(UserOrganization):
 
 # Properties to return via API, id is always required
 class UserPublic(UserBase):
-    id: uuid.UUID
+    id: int
 
 
 class UsersPublic(SQLModel):
diff --git a/backend/app/tests/api/routes/test_api_key.py b/backend/app/tests/api/routes/test_api_key.py
index 3c1f49c25..0191a594b 100644
--- a/backend/app/tests/api/routes/test_api_key.py
+++ b/backend/app/tests/api/routes/test_api_key.py
@@ -58,7 +58,7 @@ def test_create_api_key(db: Session, superuser_token_headers: dict[str, str]):
     assert "id" in data["data"]
     assert "key" in data["data"]
     assert data["data"]["organization_id"] == org.id
-    assert data["data"]["user_id"] == str(user.id)
+    assert data["data"]["user_id"] == user.id
 
 
 def test_create_duplicate_api_key(db: Session, superuser_token_headers: dict[str, str]):
@@ -101,7 +101,7 @@ def test_list_api_keys(db: Session, superuser_token_headers: dict[str, str]):
 
     first_key = data["data"][0]
     assert first_key["organization_id"] == org.id
-    assert first_key["user_id"] == str(user.id)
+    assert first_key["user_id"] == user.id
 
 
 def test_get_api_key(db: Session, superuser_token_headers: dict[str, str]):
@@ -121,7 +121,7 @@ def test_get_api_key(db: Session, superuser_token_headers: dict[str, str]):
     assert data["success"] is True
     assert data["data"]["id"] == api_key.id
     assert data["data"]["organization_id"] == api_key.organization_id
-    assert data["data"]["user_id"] == str(user.id)
+    assert data["data"]["user_id"] == user.id
 
 
 def test_get_nonexistent_api_key(db: Session, superuser_token_headers: dict[str, str]):
diff --git a/backend/app/tests/api/routes/test_project_user.py b/backend/app/tests/api/routes/test_project_user.py
index fab5f9937..85b5241ab 100644
--- a/backend/app/tests/api/routes/test_project_user.py
+++ b/backend/app/tests/api/routes/test_project_user.py
@@ -5,7 +5,7 @@
 from app.core.config import settings
 from app.models import User, Project, ProjectUser, Organization
 from app.crud.project_user import add_user_to_project
-from app.tests.utils.utils import random_email
+from app.tests.utils.utils import random_email, get_non_existent_id
 from app.tests.utils.user import authentication_token_from_email
 from app.core.security import get_password_hash
 from app.main import app
@@ -63,7 +63,7 @@ def test_add_user_to_project(
 
     assert response.status_code == 200, response.text
     added_user = response.json()["data"]
-    assert added_user["user_id"] == str(user.id)
+    assert added_user["user_id"] == user.id
     assert added_user["project_id"] == project.id
     assert added_user["is_admin"] is True
 
@@ -75,9 +75,10 @@ def test_add_user_not_found(
     Test adding a non-existing user to a project (should return 404).
     """
     organization, project = create_organization_and_project(db)
+    user_id = get_non_existent_id(db, User)
 
     response = client.post(
-        f"{settings.API_V1_STR}/project/users/{uuid.uuid4()}?is_admin=false&project_id={project.id}&organization_id={organization.id}",
+        f"{settings.API_V1_STR}/project/users/{user_id}?is_admin=false&project_id={project.id}&organization_id={organization.id}",
         headers=superuser_token_headers,
     )
 
diff --git a/backend/app/tests/api/routes/test_users.py b/backend/app/tests/api/routes/test_users.py
index 68cb3adab..ac518075e 100644
--- a/backend/app/tests/api/routes/test_users.py
+++ b/backend/app/tests/api/routes/test_users.py
@@ -8,7 +8,7 @@
 from app.core.config import settings
 from app.core.security import verify_password
 from app.models import User, UserCreate
-from app.tests.utils.utils import random_email, random_lower_string
+from app.tests.utils.utils import random_email, random_lower_string, get_non_existent_id
 
 
 def test_get_users_superuser_me(
@@ -103,10 +103,12 @@ def test_get_existing_user_current_user(client: TestClient, db: Session) -> None
 
 
 def test_get_existing_user_permissions_error(
-    client: TestClient, normal_user_token_headers: dict[str, str]
+    db: Session, client: TestClient, normal_user_token_headers: dict[str, str]
 ) -> None:
+    non_existent_user_id = get_non_existent_id(db, User)
+
     r = client.get(
-        f"{settings.API_V1_STR}/users/{uuid.uuid4()}",
+        f"{settings.API_V1_STR}/users/{non_existent_user_id}",
         headers=normal_user_token_headers,
     )
     assert r.status_code == 403
@@ -347,11 +349,13 @@ def test_update_user(
 
 
 def test_update_user_not_exists(
-    client: TestClient, superuser_token_headers: dict[str, str]
+    db: Session, client: TestClient, superuser_token_headers: dict[str, str]
 ) -> None:
+    non_existent_user_id = get_non_existent_id(db, User)
+
     data = {"full_name": "Updated_full_name"}
     r = client.patch(
-        f"{settings.API_V1_STR}/users/{uuid.uuid4()}",
+        f"{settings.API_V1_STR}/users/{non_existent_user_id}",
         headers=superuser_token_headers,
         json=data,
     )
@@ -445,10 +449,12 @@ def test_delete_user_super_user(
 
 
 def test_delete_user_not_found(
-    client: TestClient, superuser_token_headers: dict[str, str]
+    db: Session, client: TestClient, superuser_token_headers: dict[str, str]
 ) -> None:
+    non_existent_user_id = get_non_existent_id(db, User)
+
     r = client.delete(
-        f"{settings.API_V1_STR}/users/{uuid.uuid4()}",
+        f"{settings.API_V1_STR}/users/{non_existent_user_id}",
         headers=superuser_token_headers,
     )
     assert r.status_code == 404
diff --git a/backend/app/tests/conftest.py b/backend/app/tests/conftest.py
index fa36ddf0d..8ea01daca 100644
--- a/backend/app/tests/conftest.py
+++ b/backend/app/tests/conftest.py
@@ -27,8 +27,8 @@ def db() -> Generator[Session, None, None]:
         yield session
         # Delete data in reverse dependency order
         session.execute(delete(ProjectUser))  # Many-to-many relationship
-        session.execute(delete(Project))
         session.execute(delete(Credential))
+        session.execute(delete(Project))
         session.execute(delete(Organization))
         session.execute(delete(APIKey))
         session.execute(delete(User))
diff --git a/backend/app/tests/crud/collections/test_crud_collection_read_one.py b/backend/app/tests/crud/collections/test_crud_collection_read_one.py
index 6c28f31b4..22edba532 100644
--- a/backend/app/tests/crud/collections/test_crud_collection_read_one.py
+++ b/backend/app/tests/crud/collections/test_crud_collection_read_one.py
@@ -36,7 +36,7 @@ def test_can_select_valid_id(self, db: Session):
     def test_cannot_select_others_collections(self, db: Session):
         collection = mk_collection(db)
 
-        other = uuid_increment(collection.owner_id)
+        other = collection.owner_id + 1
         crud = CollectionCrud(db, other)
         with pytest.raises(NoResultFound):
             crud.read_one(collection.id)
diff --git a/backend/app/tests/crud/documents/test_crud_document_delete.py b/backend/app/tests/crud/documents/test_crud_document_delete.py
index 304dd5647..8b42451a5 100644
--- a/backend/app/tests/crud/documents/test_crud_document_delete.py
+++ b/backend/app/tests/crud/documents/test_crud_document_delete.py
@@ -33,7 +33,7 @@ def test_delete_follows_insert(self, document: Document):
     def test_cannot_delete_others_documents(self, db: Session):
         store = DocumentStore(db)
         document = store.put()
-        other_owner_id = store.documents.index.peek()
+        other_owner_id = store.documents.owner_id + 1
 
         crud = DocumentCrud(db, other_owner_id)
         with pytest.raises(NoResultFound):
diff --git a/backend/app/tests/crud/test_org.py b/backend/app/tests/crud/test_org.py
index 77ef5b46c..7efba0ec3 100644
--- a/backend/app/tests/crud/test_org.py
+++ b/backend/app/tests/crud/test_org.py
@@ -2,7 +2,7 @@
 
 from app.crud.organization import create_organization, get_organization_by_id
 from app.models import Organization, OrganizationCreate
-from app.tests.utils.utils import random_lower_string
+from app.tests.utils.utils import random_lower_string, get_non_existent_id
 
 
 def test_create_organization(db: Session) -> None:
@@ -30,7 +30,8 @@ def test_get_organization_by_id(db: Session) -> None:
 
 def test_get_non_existent_organization(db: Session) -> None:
     """Test retrieving a non-existent organization should return None."""
+    org_id = get_non_existent_id(db, Organization)
     fetched_org = get_organization_by_id(
-        session=db, org_id=999
+        session=db, org_id=org_id
     )  # Assuming ID 999 does not exist
     assert fetched_org is None
diff --git a/backend/app/tests/crud/test_project_user.py b/backend/app/tests/crud/test_project_user.py
index e5eea790c..72025ae66 100644
--- a/backend/app/tests/crud/test_project_user.py
+++ b/backend/app/tests/crud/test_project_user.py
@@ -5,7 +5,7 @@
 
 from app.crud import project_user as project_user_crud
 from app.models import ProjectUser, ProjectUserPublic, User, Project, Organization
-from app.tests.utils.utils import random_email
+from app.tests.utils.utils import random_email, get_non_existent_id
 from app.core.security import get_password_hash
 
 
@@ -111,7 +111,7 @@ def test_remove_user_from_project_not_member(db: Session) -> None:
     organization, project = create_organization_and_project(db)
 
     project_id = project.id
-    user_id = uuid.uuid4()
+    user_id = get_non_existent_id(db, User)
 
     with pytest.raises(
         ValueError, match="User is not a member of this project or already removed"
diff --git a/backend/app/tests/utils/utils.py b/backend/app/tests/utils/utils.py
index 271b338ef..2945e8b35 100644
--- a/backend/app/tests/utils/utils.py
+++ b/backend/app/tests/utils/utils.py
@@ -4,12 +4,16 @@
 
 import pytest
 from fastapi.testclient import TestClient
-from sqlmodel import Session
+from sqlmodel import Session, select
+from typing import Type, TypeVar
 
 from app.core.config import settings
 from app.crud.user import get_user_by_email
 
 
+T = TypeVar("T")
+
+
 @pytest.fixture(scope="class")
 def openai_credentials():
     settings.OPENAI_API_KEY = "sk-fake123"
@@ -40,6 +44,15 @@ def get_user_id_by_email(db: Session):
     return user.id
 
 
+def get_non_existent_id(session: Session, model: Type[T]) -> int:
+    """
+    Returns an ID that does not exist for the given model.
+    It fetches the current max ID and adds 1.
+    """
+    result = session.exec(select(model.id).order_by(model.id.desc())).first()
+    return (result or 0) + 1
+
+
 class SequentialUuidGenerator:
     def __init__(self, start=0):
         self.start = start